Method of treating reaction products of phosphates and sulphuric acid



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June 9, 1931.

METHOD OF TREATING REACTION PRODUCTS OF' PHOSPHATES AND SULPHURIC ACID AFiled Jan. 2l. 192.7

IN VEN TOR.` 01"?? S 6I?,

Patent June -1 9, l 1931 *i BJ' COLBJRNSEN, 0F GDVIKEN, NEAR STOCKHOLM,SWEDEN Application led January 21, 1927p Serial No.f162,685, and'inSweden January 23, 1926.

i. ce, (no4) 2+ naso,=

203504 'l' CHa 2- rlhe sulphuric acid used will then be lost ll@ and`the monocalcium phosphate becomes.

mixed with gypsum. c

The present invention has for its obJect a method of treating rawphosphates or substances containing phosphates (superphos-- l5 phate),which have previously been decomposed with sulphuric acid, so thatphosphates are obtained, which are soluble in citrate and -in citricacid solutions at the same time as the sulphuric acid used in thetreatment can 30 be wholly or partially recovered.

ccording to the present invention the raw phosphates, having beendecomposed inthe above mentioned manner, are treated in the form of uasuspension with ammonium car'- bonate or with ammonia and carbon dioxidesuitably at a temperature of about 40 C. and preferably during a time of4 -6 hours under stirring. By this means someone of the reactions 2 or 3or a combination of both will take place, dependent on the reactiontemperature, the quantity of ammonium car- 'bonate added and on thelength ofthe time of reaction:

v2. 03H4 2 l 2Cas04 "l" 2 2G03 2SO4+ i 03.003

3. 03H4 2 "l" 2CaSO4 2 2G03 oa3 (P04) ,e2 (NH4) 2sodaoofremo.

phate is consequently transformed intoa phosphate, whichA isy soluble incitrate and citric4 45. acid solutions and is assimilable for plants,at'the same time as the sulphuric acid, which has been used indecomposing the raw phosphate, is recovered in the form of ammoniumsulphate. v

According to the` 'reaction 3 tricalcium- According to the reaction 2dicalcium phosthus formed andthe raw phosphosphate and ammonium sulphateare formed in a similar manner. It is, however, to be observed, that thetricalcium phos hate Obtained in this manner is almost periectly solublein a 2% citric acid solution according to i/Vagner, and its value as amanure is .about the same as or better than that of ordinary Thomas orRhenania phosphate.

After the reactions 2 or 3 have been completed, the precipitate of diortricalcium phosphate, and it may be also calcium carbonate, is filteredfrom the solution of ammonium sulphate, which latter can be treated inany known manner for recovering a solid Icrystallized ammonium sulphate.The phosphate-precipitates are dried and pulverized,

whereafter they are ready to be used as a,

phosphoric acid manure.

.There are, however, other methods of treating raw phosphates, havingbeen decomposed with sulphuric acid, with ammoniurm carbonate accordingto the present invention, without departing from the principalcharacteristics of the reactions 2 and 3.-'

Thus, one may also, after the reaction 1 has been completed, treat thereaction product with lime milk or lime stone powder, so that dicalciumphosphate. is formed in a known manner according to the formula:

L 4. 2CaSO4-i- CaH4 (P04) 2 CaO 2CaSO4 2CaHPO4 -l- H2O. The precipitate.obtained in this manner Y and consisting of dicalcium phosphate and 5.acaso@L 2oaHPo4+2 (NH4) 2co3= e i 2CaHPO4 'l' 203.003 2SC.;-

The dicalcium phosphate formed according tol the reaction 4 is leftsubstantially unattacked according to the reaction 5, while thesulphuric acid, which has been used for decomposing the raw phosphate,lisstill recovered in the form of ammonium sulphate, which can berecovered in any known manner.

vThe accompanying drawing shows diagrammatically a iowsheet'in which 1desi ates the decomposition vessel, where phospinte rock and sul huricacidare added. .2 1s the reaction vesse where the reactions indrcated onthe sketch are executed. 3 1s a rotary filter, where (NHJgSOfI-HZO isseparated and evaporatedat 4 andstored up as 2S()4.- at i The phosphatesare carried over from the rotary filter `3 to the rotary drier l6 andass therefrom to the pulverizer 7 where the p osphates are pulverizedIand stored up at 8.

Further advantages, which are orcan be gained in applying theabovedescribedmethods, are'amongst others the following:

According to the reactions 2, 3 and 5 the gypsum formed when thesulphurlc acid reacts with the raw hosphates and which in ordina cases'wou d dilute the final product, is rep accd by calcium carbonate. Thisis advantageous, since the calcium carbonate, besides being easier toseparatev by filtrationthan, the psum, also has a considerabl lower moecular weight (CaCO3=100, Ca O,2aq'==172.2). This means, that thephosphate-precipltate obtained, for instance according to the reaction2, will contain a considerably higher percentage of P2()5 than that ofthe starting material. a

On starting vfrom a raw phosphate, which according to earlier methodswould for inx stance give a 20% superphosphate, it will accordingto thepresent invention be possible toobtam,I by working according to thereac-i tions 1 2 and 3,la product containing about 33% o phos horic acidsoluble in citrate and citric acid -so ution. On startlng from a rawphosphate of a considerably lower percenta e, which according to theordinary method o? manufacturing superphosphate, would give for instancea 14% superphosphate, it will be possible according to the presentinvention to obtain a product containing about 24% of assimilablephosphoric acid. l Moreover, the advantage is gained according to thepresent invention, that it is possible to start without inconveniencefrom such raw phosphates, which due to their content of iron and aluminacannot be used according to the known methods for manufacturingvsuperphosphate due to the fact, that the Iron and aluminum phosphatesformed revert the superphosphate during the storage of the product. Thephosphate-precipitates formed a"c cording to this invention are namelycompletel neutral and dry bodies, in which no secon ary reactions takeplace during the storage,

.Moreover, the present invention makes it possible to utilize raw'phosphates containing so large quantities of carbonate, that-they, dueto the t consumption of sulphun'c acid caused y said carbonates, cannotfrom economical reasons be used for manufacturing su rphosphateaccording tothe known method. According to the present invention,however, this great consumption of sulphuric acid is of no importance,as the sulphuric acid is recovered.

'As to the ammonium sulphate formed it may be observed, that the same isobtained in a completely 'neutral form, as it is recovered from a feeblyalkaline solution. Ammonium sulphate manufactured in the ordinary mannerby neutralizing sulphurio acid with ammonia always Contains traces offree sulphuric acid, which has an unfavourable action during the storageof the'same, since the ammonium sulphate thereby has a tendenc and,moreover, the free su y of. caking, phuric acid has a corrosive actionon,the packing during the storage or transportation -of the ammoniumsulphate. l

`.As )will be clear from the foregoing it is easy to establish theconditions of reaction, necessary for the llpractical execution of thepresent method.

The decomposition of raw phos hates with sulphuric acid is a process,whic is knownlong ago and which has been seriousl investigated.According to this inventlon the treatment of the product of saiddecomposition with ammonium carbonates or with ammonia and carbondioxide takes place at the' temperature of only about 40 at whichtemperature the different reactions are carried out very easily andcompletely and can be completed during an time of 4-6 hours. Thefiltering ofi' of the phosphate-precipitates alsotakes place very easilyas distinguished completely. During the course of the reactions thereare then formed further quantities ofkammonium sulphate, which at thereaction tmperature of about 40 C. will partially be dissolvedandpartially precipitated together with the phosphate-precipitates. Iftherefore, after thev treatment is completed, the temperature of themass is rapidly raised up to about 80 C. the previously precipitatedammonium sulphate will valso be dissolved, so that after filtration atan elevated temperature, and when the solution is thereafter 1 cooled,the ammonium sulphate will precipitate and is then obtained in a verypure form.`

The mother liquor, which -is filtered olf, is thereafter again used as acarrier for new quantities of ammonium carbonates and it is phate place,

only necessary to evaporate the water used for washing thephosphate-precipitates in order to recover ammonium sulphatetherefrom.

,A However, if it is desired to obtain directly a mixture of ammoniumsulphate and phossoluble in citrate and citric acid solutions, itispreferable to work in such a manner, that after the treatment withammonium carbonate or ammonia and carbon dioxide one does not heat thereacting massl but permits the new formed ammonium sulphateto remainmixed with the phosphate-precipi- `tatesin such a manner, that byfiltering the reacting mass the ammonium sulphate, which is in solution,isy separated from the solid ammonium sulphate, which remains in thephosphate-precipitates. The mixture of phosphate and ammonium sulphatecan then' be dried, so as to directly obtain an intimate mixture ofammonium sulphate and phosphate, which is soluble in citrate and citricacid solutions. B suitably l adapting the temperature, at w ich th/eiiltration takes it will thus be possible to cause a greater or smallerquantity of ammonium heating said solution so as to recover ammoniumsulphate.

In testimony whereof I havel hereunto 'aiiixed my signature. BJARNEsulphate to remam in the phosphate precip1'.v

' monia and carbon dioxide thereto, separating i composed by v withwater so as to partially disso partially suspend the same, precipitatintreating the decom the insoluble calcium salts from the solution andheating said solution so as to recover ammonium sulphate;

2. Method o treating raw phosphates desulphuric acid, which comroducttreating 'the decomposition ve and prises dicalcium phosphate therefrom,using mil of lime as precipitant, supplying ammonia and carbon dioxidethereto, separating the insoluble calcium salts from the solution andlheating said solution so asy to recover ammonum sul hate.

3. Metho of treating raw phosphates decomposed by sulphuric acid, whichcomprises osition product with water so as toV partial y dissolve andartially suspend the same, precipitating phosphate therefrom, usingcalclum carbonate as precipitant, supplying ammonia and carbon dioxidethereto, separating the insoluble calcium salts from the solution andlcalcium CoLBJRNsEN.

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